Biologics are commonly employed to promote bone growth in medical applications including fracture healing and surgical management of spinal disorders. Spine fusion is often performed by orthopedic surgeons and neurosurgeons alike to address degenerative disc disease and arthritis affecting the lumbar and cervical spine. Historically, autogenous bone grafting, commonly taken from the iliac crest of the patient, has been used to augment fusion between vertebral levels.
One protein that is osteoinductive and commonly used to promote spine fusion is recombinant human bone morphogenetic protein-2 (rhBMP-2). Its use has been approved by the US Food and Drug Administration (FDA) for single-level anterior lumbar interbody fusion. Since this time, the use of rhBMP-2 has increased significantly and expanded to include posterior lumbar spinal fusion as well as cervical spine fusion.
Oxysterols form a large family of oxygenated derivatives of cholesterol that are present in the blood, and in human and animal tissues. Oxysterols have been found to be present in atherosclerotic lesions and play a role in various physiologic processes, such as cellular differentiation, inflammation, apoptosis, and steroid production. Some naturally occurring oxysterols have robust osteogenic properties and can be used to grow bone. The most potent osteogenic naturally occurring oxysterol, 20(S)-hydroxycholesterol, is both osteogenic and anti-adipogenic when applied to multipotent mesenchymal cells capable of differentiating into osteoblasts and adipocytes.
One such oxysterol is OXY133 or (3S,5S,6S,8R,9S,10R,13S,14S,17S)17-((S)-2-hydroxyoctan-2-yl)-10,13-dimethylhexadecahydro-1H-cyclopenta[a]phenanthrene-3,6-diol, which exhibits the following structures:

To synthesize OXY133, often there are complex, multi-step chemical reactions that are difficult to carry out in a single container. For example, to synthesize OXY133 there may be utilization of various protection reagents to protect end groups as the molecule is being synthesized. In addition, various deprotection reagents are also utilized that increase cost, reduce safety and have an adverse environmental impact. Further, the route of synthesis of OXY133 can have a very low yield of less than 30%.
Recombinantly produced versions of naturally occurring human proteins, such as rhBMP-2 and rhPDGF, have been studied for decades for their ability to induce or enhance new bone formation. While these proteins have been effective in supporting bone healing, there are drawbacks with respect to the complexity of manufacturing and the associated costs. One way to address these drawbacks has been to identify small molecules that regulate parts of the bone signaling pathways to stimulate or enhance bone healing. Two examples are the osteoinductive oxysterols and statins.
Statins are inhibitors of the HMG-CoA reductase enzyme used widely for lowering cholesterol. Certain statins have also been shown to stimulate bone formation both in vitro and in vivo. Statins are thought to enhance bone formation by stimulating osteoblast differentiation and reducing osteoblast apoptosis through MAPK and TGFβ receptor signaling cascades.
Although oxysterols and statins have been shown to enhance bone healing int vivo, neither has been shown to be as potent as rhBMP-2. Therefore, despite being easier and less expensive to manufacture, their ultimate utility may be limited. Because both oxysterols and statins have been shown to have effects on bone formation and they work by different mechanisms, local co-delivery in the form of a prodrug or oxysterol-statin compound could lead to a synergistic effect greater than either delivered independently.
Therefore, there is a need for a cost effective method of synthesizing an oxysterol-statin compound for use in promoting osteogenesis, osteoinduction and/or osteoconduction. In particular, methods of synthesizing OXY133-statin compounds having a high yield and improved process safety would be beneficial. Methods for synthesizing an OXY133-statin compound, conjugate or prodrug from endogenous starting material, which is stereoselective, would also be beneficial.